High precision miniature half-cone aspirator system

ABSTRACT

In pneumatic instrumentation a miniature aspirator system in which the aspirator form is channelled in one plate of a sandwich unit, to form half-cone passages apex-to-apex. This lends itself to simple manufacturing techniques and pneumatic circuit plate assembly. An example of application is in a nozzle-baffle system, such as a control unit set point transmitter.

United States Patent Hoel L. Bowditch;

Robert C. Prescott, Foxboro; Herbert A. Neuman, Wrentham, Mass.

Nov. 1, 1968 Apr. 13, 1971 The Foxboro Company Foxboro, Mass.

Inventors Appl. No. Filed Patented Assignee HIGH PRECISION MINIATUREHALF-CONE ASPIRATOR SYSTEM 1 Claim, 16 Drawing Figs.

U.S. Cl 417/185, 417/198 Int. Cl F04f 5/16 Field of Search 103/258,

262, 263, 271274; 230/92, 95,1II, I12; I37/81.5,85,1l5;417/I85 [56]References Cited UNITED STATES PATENTS 2,952,265 9/1960 Isaacson 230/111X 3,022,743 2/1962 Engholdt 103/262X 3,450,335 6/1969 Soriano 230/953,461,895 8/1969 Colston 137/815 3,472,257 10/1969 Daruk et al. 137/81.5

Primary Examiner-Robert G. Nilson Att0rney-Lawrence H. Poeton ABSTRACT:In pneumatic instrumentation a miniature aspirator system in which theaspirator form is channelled in one plate of a sandwich unit, to formhalf-cone passages apexto-apex. This lends itself to simplemanufacturing techniques and pneumatic circuit plate assembly. Anexample of application is in a nozzle-baffle system, such as a controlunit set point transmitter.

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sum 5 or 7 PATENTED APR 1 3 1971 SHEET 7 [1F 7 llllllllll-l 0254mmMJNNOZ l wwI0z wzwo wOOO OmmvO wNwO NN OO E00 060 NOOO HIGH PRECISIONMINIATURE HALF-CONE ASPIRATOR SYSTEM This invention relates to pneumaticinstrumentation of process and energy systems, for example inmeasurement, control, recording and indicating functions.

It particularly relates to the miniaturization of such instrumentation,in modern installations requiring compactness and inclusion of more andmore sophisticated devices. One step in this direction has been theutilization of pneumatic circuit boards, providing compactness andsimplicity while maintaining and improving pneumatic circuit integrity,reliability and repeatability.

This invention provides a miniaturized aspirator system for use withmodern instrumentation, and in particular, for compatibility withpneumatic circuit board systems.

In order to achieve this aspirator system in miniature and to thenecessary high precision, this invention provides a unique half-conefrom for both the inlet and recovering cone passages. Thus, in asandwich of the order of 1 inch by onehalf inch by one-sixteenth inch,an aspirator plate is provided with two half-cone channel forms, apex toapex, with an aspirator channel transversely from the common apex pointat the throat of the aspirator. The aspirator passage forms arecompleted by a cover plate, forming the flat side of the halfcone forms.For further precision, the half-cone channels may be made with flatsides, into half-pyramid forms. Suitable passages are provided throughthe cover plate to and from the aspirator passages, and the sandwichunit may thus be side mounted on a pneumatic circuit board.

An example of an aspirator system in accordance with this inventionincludes a nozzle-bafile assembly, with a rebalancing bellows. This maybe used as a set point transmitter in a pneumatic control system, inthis example, a manually operated set point transmitter.

This flapper nozzle in a set point transmitter assembly uses thelinearizing aspirator of this invention as an output element rather thana conventional relay. Since this unit is designed to operate into smalloutput capacity, the output air delivery requirement is small. Thelinearizing aspirator reduces air consumption; yet provides linearity ofoutput vs. flapper position.

The linearizing aspirator uses the venturi principle where the flowthrough the venturi is establishedby the flapper nozzle position and theoutput pressure is obtained from a tap on the venturi throat. With a 20psi. supply to the aspirator the pressure of the venturi throat can varyfrom approximately 7 p.s.i. vacuum to greater than 17 p.s.i.g. In'therange of 3 psi. to 15 p.s.i., the relationship between flapper nozzleclearance and aspirator output pressure is essentially linear.

As the flapper position is changed, the pressure built up by theflapper-nozzle and the linearizing aspirator changes to reposition thebellows and nozzle combination to rebalance the transmitter assembly.The bellows element is calibrated 55 for a 3-- l p.s.i. output span.

Other objects and advantages of this invention will be in part apparentand in part pointed out hereinafter and in the accompanying drawings,wherein:

FIG. I is a schematic of a miniature aspirator system according to thisinvention;

FIG. 2 is a perspective of a nozzle-baffle structure;

FIG. 3 is a side view of the structure of FIG. 2, with a schematicshowing of a miniature aspirator unit therewith;

FIG. 4 is an illustration of an aspirator unit according to thisinvention, as mounted on a pneumatic circuit board;

FIG. 5 is an exploded view of one form of miniature aspirator sandwichassembly according to this invention;

FIGS. 6 through 9 are views of a miniature aspirator plate according tothis invention, respectively, outside face, edge,

Y aspirator face, and aspirator section as on line 9-9 of FIG. 8;

FIGS. 10 through 13 are enlarged views of the immediate aspirator areaof the structure of FIG. 8, respectively, FIG. 10 as top view, FIG. 11as a section on line 1ll1-of FIG. 10, FIG. 12 as a section on line 12-12of FIG. 10, and FIG. 13 as a section on line l3-l3of FIG. 10.

FIG. 14 illustrates a conical form of the structure of FIGS. 10 through13;

FIG. 15 illustrates another curved form as a variant of the structure ofFIGS. 10 through 13; and

FIG. 16 is an example of a performance graph of output pressure vs.nozzle-baffle separation in a miniature aspirator system according tothis invention.

In FIG. I, the showing comprises a miniature aspirator 10, anozzle-baffle-rebalance bellows combination l1, and mechanical linkage12.

The aspirator is provided with an air supply at 13, from which air isconducted through the aspirator by way of the inlet half-cone 14 and therecovery half-cone 15. An aspirator passage 16 is provided transverselyof this flow, at the throat of the aspirator half-cones, in theirapex-to-apex alignment point of meeting.

References to the half-cone form of the aspirator herein are intended toinclude forms in the nature of half-pyramids, trapezoids, or the like.In each case, the halves are axial, along a plane including the cone orpyramid apex, actual or in extension. Such forms may also be less thanhalf-cone or half the other forms.

The combination 11 comprises a fixed, angled support member 17 which hasa flexure 18 mounted thereon in cantilever fashion, with a mounting andpivotarea at 19. A bellows 20 has its fixed end secured to the mountingmember 17, and its movable end engaging the flexure 18, against theaction of an adjustable bias spring 21 which tends to move the flexure18 towards and against the movable end of the bellows.

A nozzle 22 is also mounted on the flexure 18 at a point near the pivotarea 19, and between the pivot area of the flexure and the contact pointof the bellows with the flexure. Thus movement of the flexure moves thenozzle in the same direction as the bellows movement, but to a lesserdegree.

A bafile arm 23 is mounted on a pivot lug 24 extending from the flexure18 on the opposite side thereof with respect to the bellows 20, andsomewhat further away from the flexure pivot area 19 than is the bellowscontact point on the flexure. The bafi'le 23 is movable about its pivot24 to variably restrict air flow from the nozzle 22. The nozzle issupplied with air flow from the aspirator recovery half-cone 15 by wayof a conduit 25 which may be a passage in a pneumatic circuit board, ormay be a flexible tube, to otherwise aid in placement of the nozzle at adistance or in a particular location. The bellows 20 is pneumaticallyconnected to the aspirator passage 16 by a conduit 26, from which anoutput passage 27 is provided.

The mechanical linkage 12 is provided for manual adjustment of thebaffle 23 about its pivot 24. This is accomplished by manual rotation ofa shaft 28. This rotation moves a sleeve 29 along a screw thread on theshaft 28, and results in rotation of an arbor 30, with consequentpivoting of the baffle 18, and movement of an indicator arm 31.

In the action of the half-cone aspirator 10, with the nozzle 22uncovered, the air flow is directly through the aspirator to the nozzle.This action draws air into the aspirator through the passage 16. Thiscan be to the degree of a negative pressure in the bellows 20. With thenozzle covered by the baffle, back pressure creates positive pressure inthe bellows and in the output 27.

The operation of the system of FIG. 1, for example as a control unit setpoint transmitter provides an accurately adjustable output. As thebaffle 23 increases the restriction of the nozzle, the bellows pressureincreases, and the baffle is moved away from the nozzle in a rebalancingeffect. This movement of the flexure by the bellows also moves thenozzle in the same direction, but less. This is convenient and simplenozzle mounting and the nozzle movement is small.

This device lends itself to use as a vacuum regulator since its outputrange extends from positive gauge pressure to a vacuum range.

FIGS. 2 and 3 structurally illustrate the nozzle-baffle-bellows systemof FIG. 1. Like reference numbers denote like elements throughout.

FIG. 4 illustrates the basic elements of the half-cone aspiratorsandwich assembly as mounted on a pneumatic circuit board 32, infragment. The main aspirator plate is indicated at 33, and a cover plate34. Suitable other sandwich elements may be used as sealing or supportdevices as needed for specific installations. The exploded view of FIG.5 further illustrates one form of an aspirator sandwich according tothis invention. An outer cover plate is shown at 35 with only mountingholes 36 therethrough. The aspirator plate is shown at 37, and an innercover plate at 38. The mounting holes 36 are common to all, and thecover plate 38 may be under surface forrned to provide a sealing contactwith the top of the aspirator plate 37. Further, the top of the coverplate 38 may be mounted against a circuit board, or, with tubeconnectors 39, may be otherwise connected into suitable pneumaticcircuitry.

The various views of the aspirator plate and the aspirator area in theplate shown in FIGS. 6 through 13 detail the specific formations of theaspirator as generally a half-cone aspirator, and specifically in FIGS.through 13, as a halfpyramid aspirator with a rectangular slottransverse aspirator passage.

FIGS. 14 and 15 respectively illustrate a true conical form, and acurved variant between the true cone and the form of FIG. 13, asexamples of alternative structures according to this invention.

The miniature nature of the aspirator and its sandwich plate form, isshown in that the sandwich unit may be less than 1/16 thick.

The perfonnance curve of FIG. 16 emphasizes the effectiveness of theminiature aspirator according to this invention, both as to linearityand as to ability to aspirate in the region of negative pressure.

This invention therefore provides a new and useful pneumaticinstrumentation system component in the form of an aspirator formed aspart of a cone, pyramid, trapezoid or the like. This can beaccomplished, for example, by plastic molding.

We claim:

1. A manually operated pneumatic set point transmitter comprising:

a fixed support with a base and a side;

an arm flexibly mounted on the top of said support side and extendingover said base as a cantilever;

a nozzle secured to said cantilever arm adjacent said flexible mountingand said support side;

a bellows having one end fixed to said support base and the other endwith means engaging said cantilever arm to flex said am away from saidbase upon expansion of said bellows;

a spring connecting the outer end of said cantilever arm with said baseand holding said arm against said bellows engaging means;

a pivot boss secured to the outer face of said cantilever arm at a pointbetween said spring and said bellows engaging means;

a lever pivotally mounted to said pivot boss and extending along saidcantilever arm to restrictably overlie said nozzle;

manually adjustable linkage means for adjusting said nozzle restrictionby moving said lever and simultaneously indicating said manualadjustment; and a pneumatic system comprising an aspirator, an airsupply to said nozzle through said aspirator, a pneumatic connectionfrom the throat of said aspirator to the interior of said bellows, and apneumatic output from said connection;

said aspirator comprising a plate with an input slot tapered smaller into the throat of said aspirator, an output slot tapered larger out fromthe throat of said aspirator, a side access slot from said throat, and aflat sandwich plate covering said slots to form pneumatic passagesthereof.

1. A manually operated pneumatic set point transmitter comprising: afixed support with a base and a side; an arm flexibly mounted on the topof said support side and extending over said base as a cantilever; anozzle secured to said cantilever arm adjacent said flexible mountingand said support side; a bellows having one end fixed to said supportbase and the other end with means engaging said cantilever arm to flexsaid arm away from said base upon expansion of said bellows; a springconnecting the outer end of said cantilever arm with said base andholding said arm against said bellows engAging means; a pivot bosssecured to the outer face of said cantilever arm at a point between saidspring and said bellows engaging means; a lever pivotally mounted tosaid pivot boss and extending along said cantilever arm to restrictablyoverlie said nozzle; manually adjustable linkage means for adjustingsaid nozzle restriction by moving said lever and simultaneouslyindicating said manual adjustment; and a pneumatic system comprising anaspirator, an air supply to said nozzle through said aspirator, apneumatic connection from the throat of said aspirator to the interiorof said bellows, and a pneumatic output from said connection; saidaspirator comprising a plate with an input slot tapered smaller in tothe throat of said aspirator, an output slot tapered larger out from thethroat of said aspirator, a side access slot from said throat, and aflat sandwich plate covering said slots to form pneumatic passagesthereof.